Field of the Invention
The invention relates to cases for handheld electronics with antibacterial properties, and more particularly, to cases made with materials containing silver-based nanoparticles.
Description of the Related Art
Cases can be added to handheld electronic devices for protection, ornamentation, personalization, and added utility (e.g. pockets, clips, and auxiliary batteries). Typically, the cases are made from a molded resin. In some instances, the polymer may be a thermoset in others a thermoplastic.
Polycarbonate is an example of a polymer used to make cases. Polycarbonate is a tough plastic used in a variety of goods, from bulletproof windows to CDs. It has enormous strength and is simultaneously lightweight and protective. Polycarbonate cases are often a bit bulky and typically do not provide the best aesthetics.
Polymers including carbon fibers are an alternative to polycarbonate. Carbon fiber can offer good protection depending on the cases design and thickness. While carbon fiber is durable, lightweight, and looks good, it is more expensive than other polymers.
Silicone is a third common material for cases. Silicon cases are useful for preventing scrapes, minor dings, and low impact drops. Silicone is an inexpensive material. Silicone cases are typically flexible. Silicone cases can add a good grip and a tacky feel to a handheld electronic device.
Thermoplastic polyurethane or TPU can be used to form cases. TPU provides a good grip and more shock protection and durability compared to silicon.
A Wall Street Journal article titled, “Calling all Germs” reported the problem of bacteria on mobile telephones. The article cited a study. A lab tested eight randomly selected phones from an office. The phones showed no signs of E. coli or staphylococci bacteria. But all phones showed abnormally high numbers of coliforms, a bacteria indicating fecal contamination. Of the eight phones tested by HML Labs of Muncie, Ind., there were between about 2,700 and 4,200 units of coliform bacteria. In drinking water, the limit is less than 1 unit per 100 ml of water.
The problem is exacerbated by manufactures of wireless devices voiding the device's warranty after the device has been cleaned with most antibacterial cleaners. APPLE®'s handheld device manual explicitly forbids the use of “window cleaners, household cleaners, aerosol sprays, solvents, alcohol, ammonia or abrasives.” BLACKBERRY®'s advice is similar. Its manual states: “Do not use liquid, aerosol cleaners, or solvents on or near your BLACKBERRY® device.”
To create antibacterial cases, additives have been incorporated in the polymer. Prior additives to wireless cases have been banned from the market or not satisfactory. Additives such as organic chlorine, quaternary ammonias, TRICLOSAN®, among others are bacteria-dynamic (antibacterial effect uncontrolled) and some others have already been banned from the market.
Handheld electronics include electronic devices that are to be operated with a hand of the user. Examples include mobile telephones, tablet computers, laptop computers, keyboards, telephones, pagers, game controllers, and remote controls.
Wiping an electronic device before use is not an acceptable solution. First, while microfiber cloths work great to remove oil and dirt, some bacteria remain. For some of the bacteria, you only need to ingest as few as ten (10) organisms to get sick. Second, the inconvenience of carrying a cleaning cloth and wiping down a device before each device is not acceptable to most users.
An example of a silver-containing nanoparticle dispersion is commercially available from TNS under the trade name NpAg_925. NpAg_925 is a dispersion based on silver nanoparticles and water. The dispersion is effective against bacteria (both gram-positive and gram-negative bacteria), as assessed against the standard antibacterial JIS Z 2801.
The production of nanoparticles is done through a chemical process inside reactors. A process called bottom top up where reducer and stabilizer agents are used to produce stable nanoparticles and monocomponents which create the product NpAg_925_SiO. To produce the powder compound the nanoparticles return to the reactor with ceramic powder in an order of 5 μm and food grade.
NpAg_925 is a colloidal dispersion of metallic silver in an aqueous medium, stabilized with organic molecules. The dispersion is a nonionic yellowish brown liquid that is soluble in water. The dispersion has a density of approximately 1.0 g/cm3 at 25° C. The dispersion has a pH value of approximately 4.0. The solid content is about 1000 ppm.
The dispersion is compatible with additives and compounds based on water. The nanoparticles have an average size of 10 nm. The size range is 15-20 nm. The maximum wavelength is 400-410 nm.
NpAg_925 is a customized, monolithic antimicrobial product that can be applied in different segments. This is an aqueous emulsion containing silver nanoparticles stabilized with special organic molecules that ensure safe and effective application. The NpAg_925 product is nontoxic, easy to handle and to apply. The NpAg_925-SiO is an inorganic compound that functions as antibacterial developed with additives based on nanoparticles of metallic silver. It is classified as a bacteriostatic product designed to inhibit the formation and growth of pathogenic microorganisms.
The NpAg_925-SiO is suitable for incorporation into polymer matrices and ink formulations. During the application of the product it is necessary to ensure proper homogenization of the additive in the matrix in which it is added. Avoid contact with moisture and clumping of the granules so as to not result in problems of homogenization.
The quantity of NpAg_925-SiO to be added depends on the polymer matrix and the specific needs of each application.
The NpAg_925-SiO composition is made from the following components.
COMPOSITIONCAS NUMBER% BY WEIGHTH2O7732-18-5 98.0-99.4%AminosilaneConfidential0.5-5.0Ag7440-22-40.1-2.0
Other compatible silver nanoparticles are available under the following trade names: Santaized and Microban.